There are communication apparatuses having functions of performing communication through a telephone network via a switch board such as a telephone function and a facsimile function (hereinafter referred to as “telephone-network communication function”). These communication apparatuses generally have a main power-supply circuit for supplying various units in the apparatus with electric power. For example, in a multifunction peripheral, when a power switch is turned on, the main power-supply circuit supplies electric power to various units in the apparatus, such as a print mechanism, a copy mechanism, a DAA (Data Access Arrangement) and a modem.
Recently, for reducing power consumption, various electrical equipment including communication apparatuses is provided with, as operational modes, a normal mode in which the main power-supply circuit can supply various units with electric power and a sleep mode in which power supply from the main power-supply circuit is stopped except that micro power is supplied to a requisite minimum circuit such as a control circuit.